Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
  • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
  • H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
  • H04B7/0617—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal for beam forming
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/0413—MIMO systems
  • H04B7/0426—Power distribution
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/0413—MIMO systems
  • H04B7/0456—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/0413—MIMO systems
  • H04B7/0456—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
  • H04B7/046—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting taking physical layer constraints into account
  • H04B7/0465—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting taking physical layer constraints into account taking power constraints at power amplifier or emission constraints, e.g. constant modulus, into account
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
  • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
  • H04B7/0667—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of delayed versions of same signal
  • H04B7/0671—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of delayed versions of same signal using different delays between antennas
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
  • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
  • H04B7/068—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission using space frequency diversity
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
  • H04B7/0697—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using spatial multiplexing
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
  • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
  • H04L25/03891—Spatial equalizers
  • H04L25/03898—Spatial equalizers codebook-based design
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L5/00—Arrangements affording multiple use of the transmission path
  • H04L5/0001—Arrangements for dividing the transmission path
  • H04L5/0014—Three-dimensional division
  • H04L5/0023—Time-frequency-space
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/26—Systems using multi-frequency codes
  • H04L27/2601—Multicarrier modulation systems
  • H04L27/2626—Arrangements specific to the transmitter only
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/26—Systems using multi-frequency codes
  • H04L27/2601—Multicarrier modulation systems
  • H04L27/2647—Arrangements specific to the receiver only

Definitions

• the present invention generally relates to radio communication systems, devices, software and methods and, more particularly, to mechanisms and techniques for combining precoding and cyclic delay diversity associated therewith.
• LTE Long Term Evolution
• OFDM orthogonal frequency division multiplexing
• FDMA single carrier frequency division multiple access
• Such techniques include, for example, diversity against fading (e.g.. spatial diversity), shaping the overall antenna beam to maximize gain in the direction of the target (beamforming), and the generation of what can be seen as multiple, parallel "channels' * to improve bandwidth utilization (spatial multiplexing or multi-input multi- output (MIMO).
• diversity against fading e.g.. spatial diversity
• beamforming shaping the overall antenna beam to maximize gain in the direction of the target
• MIMO multi-input multi- output
• Precoding is a popular technique used in conjunction with multi-antenna transmission.
• the basic principle involved in precoding is to mix and distribute the modulation symbols over the antennas while potentially also taking the current channel conditions into account.
• Precoding can be implemented by, for example, multiplying the information carrying symbol vector containing modulation symbols by a matrix which is selected to match the channel. Sequences of symbol vectors thus form a set of parallel symbol streams and each such symbol stream is referred to as a "layer".
• a layer may directly correspond to a certain antenna or a layer may. via the precoder mapping, be distributed onto several antennas.
• Cyclic delay diversity is a form of open-loop precoding in which the precoding matrix is intentionally varied over the frequency within the transmission (or system) bandwidth. Typically, this is realized by introducing different cyclic time delay for the different antennas, or alternatively realized by varying the phase of the transmitted signals from the different antennas. This kind of phase shift means that the effective channel, comprising the true channel and the CDD precoding. varies faster over frequency than the original channel. By distributing the transmission over frequency, this kind of artificially induced frequency-selectivity is useful in achieving frequency diversity.
• the channel rank can vary from one up to the minimum of number of transmit and receive antennas. For example, given a 4x2 system as an example, i.e.. a system with four transmit antennas and two receive antennas, the maximum channel rank is two.
• the channel rank associated with a particular connection varies in time and frequency as the fast fading alters the channel coefficients.
• the channel rank determines how many layers, also referred to as the transmission rank, can be successfully transmitted simultaneously.
• the channel rank is one at the instant of the transmission of two layers, there is a strong likelihood that the two signals corresponding to the two layers will interfere so much that both of the layers are erroneously detected at the receiver.
• adapting the transmission to the channel rank involves striving for using as many layers as the channel rank.
• Figure 1 illustrates a transmission structure 108 for combining CDD and. possibly channel dependent, precoding.
• each layer 1 10 created by the transmitter presents a stream of information carrying modulation symbols to the CDD based precoder 112 as a sequence of symbol vectors 1 14.
• the CDD precoder 1 12 applies the two matrices 1 16 and 1 18 illustrated therein to each incoming symbol vector to perform the precoding process. More specifically, the CDD precoder 1 12 first applies the
• U N 7 xr matrix 118 is a column subset of a (possibly scaled) unitary matrix, r denotes the transmission rank and N 1 is the number of transmit antennas in the transmitting device.
• the notation TM-k ⁇ l means a matrix A having k rows and / columns.
• the diagonal CDD matrix 1 16 has non-zero values along the diagonal including an antenna phase shift value ⁇ indexed by a parameter k which may be a function of frequency.
• k may e.g. represent the subcarrier index or the closely related data resource element index (which excludes resource elements containing reference symbols). It should also be noted that k may be a more arbitrary function of the position of the resource elements on the resource grid in OFDM.
• the resulting, precoded modulation symbol vector is then output for. e.g.. resource mapping and OFDM modulation 120. prior to being transmitted via antennas 122 (also referred to as antenna ports).
• the transmission structure 108 illustrated in Figure 1 can be utilized in several ways. For example, one option is to use a fixed, channel independent, unitary matrix U N T xr 1 18 with a certain number of columns r corresponding to the transmission rank.
• the unitary matrix 1 18 serves to distribute each symbol on all antennas 122, while the diagonal CDD matrix 1 16 varies (shifts) the phase of each antenna 122. This increases the frequency selectivity of the effective channel each layer 1 10 experiences which, as mentioned above, can be useful for achieving frequency diversity (as well as multi-user diversity when frequency domain scheduling is used).
• this column together with the diagonal CDD matrix 116, forms a frequency selective beamformer which may be varied in a periodic fashion over the scheduled bandwidth. The period will depend on the selected speed of lhe phase variations. However, such beamforming may be problematic because, if the MIMO channel is correlated at the transmit side, severe cancellation of signals may occur at some frequencies. If the coding rate is not low enough over the scheduled bandwidth, this will in turn result in communication errors. Similar cancellation can occur even for transmission ranks greater than one.
• a method for transmitting information signals having a plurality of symbol vectors associated therewith on a radio channel includes precoding the symbol vectors by multiplying the symbol vectors with: a first column subset of a unitary matrix which spreads symbols in the symbol vectors across all virtual transmit antennas, a second diagonal matrix which changes a phase of the virtual transmit antennas, and a third precoding matrix which distributes transmit energy across physical transmit antennas, further processing the precoded symbol vectors to generate the information signals, and transmitting the information signals.
• a transmitter for transmitting information signals having a plurality of symbol vectors associated therewith on a radio channel includes: a plurality of physical transmit antennas, a processor for precoding the symbol vectors by multiplying the symbol vectors with: a first column subset of a unitary matrix which spreads symbols in the symbol vectors across all virtual transmit antennas, a second diagonal matrix which changes a phase of the virtual transmit antennas, and a third precoding matrix which distributes transmit energy across the physical transmit antennas, and for further processing the precoded symbol vectors to generate the information signals: and a transmit chain of elements for transmitting the information signals.
• a method for equalizing received information signals having a plurality of symbol vectors associated therewith includes forming a channel estimate associated with the received information signals by multiplying an initial channel estimate with a plurality of matrices, the plurality of matrices including: a first column subset of a unitary matrix, a second diagonal matrix, and a third precoding matrix, and equalizing the information signals using the formed channel estimate.
• a processor forms a channel estimate associated with received information signals by multiplying an initial channel estimate with a plurality of matrices, the plurality of matrices including: a first column subset of a unitary matrix, a second diagonal matrix, and a third precoding matrix, and wherein the processor uses the formed channel estimate to equalize the received information signals.
• Figure 1 illustrates a transmission structure including a conventional precoder
• FIG. 2 illustrates an exemplary LTE access network in which exemplary embodiments can be implemented:
• Figure 3 depicts exemplary LTE physical layer information signal processing with which exemplary embodiments can be associated;
• FIG. 4 shows an example of an antenna mapping function in more detail
• Figure 5 illustrates a transmission structure including a precoder according to an exemplary embodiment
• FIG. 6 is a block diagram of an exemplary transmitting device in which precoding according to these exemplary embodiments can be implemented:
• Figure 7 is a flowchart illustrating a method for transmitting information signals according to an exemplary embodiment:
• Figure 8 is a block diagram of an exemplary receiving device in which signals which have been precoded according to these exemplary embodiments can be processed.
• Figure 9 is a flowchart illustrating a method for processing received information signals according to an exemplary embodiment.
• the transmission structure 108 illustrated in Figure 1 and, more particularly, the CDD precoder 1 12. suffer from certain drawbacks when considering its applicability in the context of matrices 1 18 which are channel independent.
• another problem with the transmission structure 108 can occur if channel dependent precoding is to be used in conjunction with CDD. Since the diagonal CDD matrix 1 16 is applied to the symbol vector 1 14 before the. in this example, channel dependent precoding matrix 1 18, the precoding matrix 1 18 will then need to deal with a more frequency-selective effective channel, i.e., comprising the true channel and the applied CDD diagonal matrix 118.
• the precoder 1 12 must then switch the elements representing matrix 1 18 at a finer frequency granularity than if only the original channel was present. This, in turn, may lead to substantially higher signaling overhead because the precoder elements which are used to precode transmitted symbols are typically identified to the receiver in the form additional (overhead) signaling.
• x(*) W ⁇ , w (*)D(*)U /xr s(*) (1)
• O(k) is the second diagonal CDD matrix 516 and it is emphasized that the third precoding matrix 515.
• W A , y (£) . may potentially be different for different values of k.
• the parameter / would here typically be set to equal the transmission rank r.
• These exemplary embodiments can be used to. for example, add a channel dependent precoding stage directly at the input of the true channel (i.e., outputting onto the antenna ports), which in turn allows CDD to be combined with channel dependent precoding without requiring finer precoding granularity, thus saving signaling overhead. Even if the third precoding matrix is not channel dependent, the structure indicated by the exemplary embodiments provides additional freedom in selecting suitable precoders for the third precoding stage so as to avoid some of the previously mentioned problems associated with the use of the structure 108.
• CDD and precoding according to these exemplary embodiments, consider first the exemplary radiocommunication system illustrated in Figures 2-4. Beginning with the radio access network nodes and interfaces in Figure 2, it will be seen that this particular example is provided in the context of LTE systems. Nonetheless, the present invention is not limited in its applicability to transmitters or transmissions associated with LTE systems and can instead be used in any system wherein multiple transmit antennas and precoding are employed, including, but not limited to Wideband Code Division Multiple Access (WCDMA).
• WCDMA Wideband Code Division Multiple Access
• GSM Wideband Code Division Multiple Access
• UTRA E-UTRA. High Speed Packet Access (HSPA), UMB. WiMaX and other, systems, devices and methods. Since, however, the example in Figure 2 is provided in terms of LTE.
• each eNodeB 200 is responsible for transmitting signals toward, and receiving signals from, one or more cells 202.
• Each eNodeB includes multiple antennas, e.g., 2, 4, or more transmit antennas, and handles functions including, but not limited to coding, decoding, modulation, demodulation, interleaving, de-interleaving, etc., with respect to the physical layer of such signals.
• transmit antennas' 1 as used herein is specifically meant to include, and be generic to. physical antennas, virtual antennas and antenna ports.
• the eNodeBs 200 are also responsible for many higher functions associated with handling communications in the system including, for example, scheduling users, handover decisions, and the like.
• the interested reader who desires more information regarding transmit or receive functions associated with LTE or other systems in which these exemplary embodiments may be deployed is directed toward the book entitled "3G Evolution - HSPA and LTE for Mobile Broadband ' ', to Erik Dahlman et aL published by Elsevier Ltd.. 2007. the disclosure of which is incorporated by reference.
• the hybrid automatic retransmission request (HARQ) steps 306 operate to extract or repeat code bits from the blocks of code bits provided by the channel encoder to generate a precise set of bits to be transmitted within a transmit time interval (TTl). e.g., based upon various criteria such as the number of assigned resource blocks, the selected modulation scheme and the spatial multiplexing order.
• Tl transmit time interval
• step 308 the code words output from the HARQ block are scrambled
• the selected data modulation e.g.. Quadrature Phase-Shift Keying (QPSK), 16 Quadrature Amplitude Modulation (QAM), or 64 QAM
• QPSK Quadrature Phase-Shift Keying
• QAM 16 Quadrature Amplitude Modulation
• 64 QAM 64 QAM
• an antenna port corresponds to the transmission of a particular downlink reference signal which may, or may not, correspond to an actual, physical antenna.
• the symbols to be transmitted on each antenna (1-n in Figure 3, e.g., 2. 4, 8, 16) are then mapped to respective resource blocks 314 and sent off for OFDM processing (not shown) prior to transmission by the eNodeB 200.
• the antenna mapping process can be further subdivided into layer mapping of the codewords output from the modulation block 310 and precoding of the resulting symbol vectors to generate the antenna (or antenna port) mapped symbols, as shown in Figure 4.
• layer mapping function 400 Therein an example is provided with two sets of codewords being mapped by layer mapping function 400 into three layers. Two symbol vectors vl and v2 associated with the three layers are illustrated in Figure 4. These symbol vectors are then precoded by applying one or more precoding matrices by precoding function 402. i.e., by matrix multiplication of the precoding matrix or matrices with the incoming symbol vectors.
• the precoding function 402 can apply three different matrices as will be described below with respect to Figure 5. It will be appreciated that the selections of mapping to three layers and four antennas in Figure 4 is purely exemplary. Selection of the number of layers will, as described earlier, vary based upon the channel rank (among possibly other criteria) and the number of antennas may vary from system to system or even among transmit devices within systems.
• Figure 5 illustrates a precoder according to exemplary embodiments which can be used to perform precoding, e.g.. as described w ith respect to blocks 312 and 402 above.
• the CDD precoder 512 applies the three matrices 515, 516 and 518 illustrated therein to each incoming symbol vector to perform the precoding process. More specifically, the CDD
• precoder 512 first applies the matrix U txr 518, which is a column subset of a possibly scaled unitary / x / matrix, to the symbol vector 514, followed by diagonal CDD matrix 516, followed then by a precoding matrix
• the columns of the matrix 518 are taken from a possibly scaled unitary matrix.
• a unitary matrix exhibits the property that its inverse is equal to the complex conjugate transpose of the unitary matrix of interest.
• the columns of the matrix 518 are orthogonal and of equal norm.
• the first applied, matrix 518 operates to spread the symbols across the antenna ports.
• the second applied CDD matrix 516 will have the qualities of a diagonal matrix, i.e.. elements on one diagonal are non-zero and the remaining matrix elements are zero.
• This CDD matrix 516 operates to vary (shift) the phase of each antenna or antenna port 522.
• the third applied, precoding matrix 515 operates to distribute the transmission energy across the antennas or antenna ports.
• It may be determined in either a channel independent manner or based upon, at least in part, current radio channel conditions resulting in a channel dependent precoder operation.
• application of these matrices to the incoming symbol vectors can be performed by a processing unit within the transmitter by way of matrix multiplication.
• the parameter / is introduced in this exemplary embodiment as a size parameter of the three matrices used to perform precoding. i.e.. the number of columns in the last applied precoding matrix 515. lhe number of rows and columns in the second applied, diagonal CDD matrix 516 and the number of rows in the first applied, unitary matrix 518.
• the size of the matrices involved in performing precoding according to these exemplar)' embodiments may vary dynamically for a given transmitter according to the transmission rank of the channel (or the number of layers), e.g., the number of rows in the unitary matrix 518 may be different than the number of transmit antennas.
• the parameter / is typically set equal to the transmission rank r.
• the matrices 1 16 and 1 18 discussed above with respect to Figure 1 were fixedly sized to the number of transmit antennas associated with the particular transmitter performing the precoding.
• the matrix U lxr 518 is, like matrix 118, a column subset of a (possibly scaled) unitary matrix where / denotes the number of rows in the matrix and r denotes the transmission rank and number of columns.
• the diagonal CDD matrix 516 includes exp(j ⁇ n k) elements along the diagonal wherein ⁇ n represents a phase value associated with a particular antenna or antenna port and k is an index associated with a particular resource element (e.g. indices of all subcarriers or indices of only those subcarriers which carry data rather than those which carry reference symbols).
• the matrix W ⁇ , ⁇ x/ 515 is a precoding matrix which can have various values. e.g.. to perform channel dependent beamforming or precoding in a channel independent manner, some examples of which are described below, and which has a size of N ⁇ (the number of transmit antennas / antenna ports in the transmitting device) by /.
• the resulting, precoded modulation symbol vector is then output for, e.g., resource mapping and OFDM modulation 520, prior to being transmitted via antennas 522.
• Uj xr can then be used to perform CDD operation on the new, improved, effective
• the number of rows / can moreover be adapted so that CDD operation is only performed among the virtual antennas taken as
• rank two could be two, ⁇ 7 /xr could have two columns, and ⁇ N, X / could be channel
• the three matrices 515, 516 and 518 could, for example, be selected from the following table:
• variables a, b, c, d, e, f, g, h, k, I, m. and n represent, potentially complex, values which are selected to provide the functions or matrix-types described above, resulting in a so-called precoder codebook. Examples of these values can be found in, for example, the standards specification 3GPP TS 36.21 1 Vl .3.1 , (2007-08). at section 6.3.3.2.
• precoding as described above and illustrated in Figure 5.
• beamforming on the virtual antennas (antenna ports) spreads energy in designated sub-spaces, which sub-spaces focus the transmission energy toward the intended recipient (e.g., mobile station) of the transmission.
• Channel independent precoding is also possible in for example the sense of varying the selection of precoders in a more random manner so as to avoid focusing the energy in any particular direction.
• a transmission structure [0041] According to another exemplary embodiment, a transmission structure
• the precoding matrix 515 i.e.. " Jv 7 x/ > is instead set to be a fixed channel and frequency independent matrix with orthogonal and equal norm columns
• the diagonal CDD matrix set to be of size Nj x Nr i.e.. a square matrix equal to the number of transmit antennas
• the matrix 518 £/ /xr can then be a single column of all ones.
• This exemplary embodiment provides another form of CDD which does not suffer from the previously mentioned cancellation problem when correlated fading is present on the transmit side.
• the transmit processing techniques described herein may be used for various communication systems such as Code Division Multiple Access (CDMA) systems. Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems. Orthogonal FDMA (OFDMA) systems, Single-Carrier FDMA (SC-FDMA) systems, etc.
• the transmitter may. for example, be disposed within a radio base station. NodeB. eNodeB, or the like, to transmit information signals on a downlink radio channel.
• the transmitter may, for example, be disposed in a mobile unit, terminal device, user equipment, or the like to transmit information signals on an uplink radio channel.
• the transmit device will typically include the components illustrated generally in Figure 6.
• the transmitter includes a plurality of physical transmit antennas
• transmit antennas 602 in this example numbering four, although more or fewer than four transmit antennas can be used.
• the physical transmit antennas 602 are connected to a processor 606 via transmit (TX) chain elements 604 which can include one or more of filters, power amplifiers and the like, as will be appreciated by those skilled in the art.
• TX transmit
• Processor(s) 606. in conjunction with memory dcvicc(s) 608 (and potentially other devices not shown) can operate to perform the transmit processes discussed above with respect to Figures 3-5, e.g., by way of software stored therein, additional hardware or some combination of software and hardware.
• the precoding functionality described above can, for example, be performed in software by executing computer-readable instructions from memory device 608 to perform the matrix multiplications described above with respect to Figure 5.
• exemplary embodiments also relate to software, e.g., program code or instructions which are stored on a computer-readable medium and which, when read by a computer, processor or the like, perform certain steps associated with transmitting information signals which are precoded in the manner described above.
• An example of such steps is illustrated in the flowchart of Figure 7.
• symbol vectors are precoded by multiplying them with a first unitary matrix which spreads symbols in the symbol vectors across the virtual transmit antennas, a second diagonal matrix which changes a phase of the virtual transmit antennas, and a third precoding matrix which distributes the transmission across the transmit antennas. After precoding the symbol vectors, they can undergo further processing at step 702 to generate information signals.
• such additional signal processing can include mapping precoded symbols to resource blocks to be transmitted via at least one of the transmit antennas and orthogonal frequency division multiplexing (OFDM) the resource blocks, although other processing, e.g., for non- OFDM systems, could alternately be performed downstream of the precoding operation.
• OFDM orthogonal frequency division multiplexing
• Exemplary embodiments also provide for receive side processing of signals which have been transmitted using the foregoing exemplary precoding embodiments. In systems using common pilots (common reference symbols (RS)). the receiver needs to be aware of the transmission structure in order to be able to properly decode the transmission. LTE is one example of such a system where this transmission mode is using common reference symbols and is thus not transparent to the UE.
• RS common reference symbols
• H is a channel estimate obtained from the common RS
• the receive side processing will essentially provide a mirrored processing to that performed on the transmit side.
• the receiver will use its knowledge of the precoding performed by the transmitter to perform its channel estimation/equalization function. Such knowledge on the part of the receiver may be predefined a priori or it may be passed on to the receiver explicitly as part of the transmitted information.
• an exemplary receiver 800 for receiving and processing information signals which have been precoded as described above is illustrated in Figure 8.
• one (or more) receive antennas 802 receive the information signals which have been precoded during transmit side processing.
• processor(s) 806 After passing through one or more receive (RX) chain processing elements 804 (e.g. filters, amplifiers or the like), processor(s) 806 will process the received information signals to extract the information contained therein, e.g., in conjunction with processing software stored on memory' device(s) 808, by using its knowledge of the precoding performed on those information signals to calculate a channel estimate used in subsequent receive side processing.
• RX receive chain processing elements 804
• processor(s) 806 will process the received information signals to extract the information contained therein, e.g., in conjunction with processing software stored on memory' device(s) 808, by using its knowledge of the precoding performed on those information signals to calculate a channel estimate used in subsequent receive side processing.
• a method for equalizing received information signals includes the steps of forming a channel estimate associated with the received information signals by multiplying an initial channel estimate with a plurality of matrices, the plurality of matrices including a first column subset of a unitary matrix, a second diagonal matrix, and a third precoding matrix at step 900, and equalizing the information signals using the formed channel estimate at step 902.
• embodiments also include ⁇ y 7 . x/ and U txr matrices of more general form and. potentially, also a more general form of CDD matrix, e.g., not limited to a diagonal matrix.
• ⁇ y 7 . x/ and U txr matrices of more general form and. potentially, also a more general form of CDD matrix, e.g., not limited to a diagonal matrix.

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